This invention relates to a coating containing polyolefins for a roofing and waterproofing sheet (felt) which can be durably heat-sealed with oxidized bitumen.
It is customary today to produce roofing and waterproofing sheet by saturation/impregnation and/or coating of a reinforcement material of inorganic or organic fiber material or sheetings with polymer-modified meltable bituminous material. A distinction is made according to DIN 52 130 V (draft July 1983) and DIN 52 131 V (draft July 1983) between elastomer-modified and plastomer-modified sheets. Elastomer-modified sheets generally contain coatings formed from mixtures of elastomers, e.g., SBS block copolymers, with bitumen. Plastomer-modified sheets generally contain coatings formed from mixtures of thermoplastic polyolefins with straight-run bitumen. Polyolefins which are generally used are the so-called atactic polypropylenes (and copolymers, generally ethylene-propylene copolymers), as they are produced as by-products in the production of the so-called isotactic polypropylenes, i.e., homo- and co-polymers, at times mixed with isotactic polypropylene. The added amount of polyolefins generally is 25 to 40% by weight. The polyolefin-modified bitumen has outstanding high resistance to aging.
The polyolefin-modified roofing sheets are generally produced in such a thickness, e.g., 4 mm and more, that they can be superficially liquefied by flaming with a gas burner (torching), thereby heat-sealing themselves and with the underlayer. Most European guidelines for the design of flat roofs prescribe a two-layer system when using bituminous sheets for the roofing. For reasons of cost, for the underlayer, which is not exposed to weathering, a conventional roofing felt prepared from oxidized bitumen often would be used and a torching sheet of polymer-modified bitumen would be used for the upper layer exposed to weathering. Torching of a polymer-modified sheet to an existing, older roofing membrane made from oxidized bitumen is also often used in repairing leaky roofs.
Experience has shown that although a polyolefin-modified roofing felt can indeed be heat-sealed to a roofing sheet impregnated with oxidized bitumen (grades 100/25 and 100/40 according to DIN 1995, which correspond to ASTM asphalt graded Type IV and Type III, respectively, being used predominantly), which is often used on roofs, over time the heat-sealing loses its initial tenacity with the formation of a greasy interlayer. As a result, the use of polyolefin-modified roofing sheets, which otherwise exhibit basically desirable properties, is now limited to situations where heat-sealing to a roofing sheet or felt of oxidized bitumen is not required, e.g., loose laying under a ballasting and roofs of two layers of polyolefin-modified bitumen.
Addition of rubber to mixtures of amorphous polyolefins and bitumen are known in the art. However, they are used only for improving mechanical properties such as elasticity, elongation at rupture, and low temperature flexibility, for which other types of rubber become necessary, than for stabilizing the heat-sealing with oxidized bitumen.
Thus, BE Patent No. 813 416 describes mixtures of an ethylene-propylene rubber, polyolefins and bitumen, in which the rubber is used for improving the mechanical resistance. However, it is a random rubber ("copolymere au hasard") in which the diene content expressly plays no role. The use according to the invention of a strongly unsaturated sequence EPDM runs diametrically counter to the teaching of this patent specification. Further, it is not to be gathered from this specification that the mixtures are suitable for producing coatings according to the invention.
U.S. Pat. No. 3,669,918 also teaches that ethylene-propylene copolymers of the random type are used for improving the flexibility and toughness of the bitumen. But mixtures of the type according to the invention are not described there.
Finally, U.S. Pat. No. 4,420,524 claims an improved prefabricated, multilayer roofing membrane with an impregnating material, which besides bitumen can contain atactic polypropylene and an amorphous copolymer of ethylene and propylene. However, this amorphous copolymer is not at all the commonly marketed EPM or EPDM, but a by-product of polypropylene copolymer production, for which there was no use up til now. Further, the object of this U.S. patent is a multilayer sheet, which is laid as a single-ply membrane and thus the problem of heat-sealing to an existing layer of oxidized bitumen is not involved.